1. Field of the Invention
The invention relates to a board-stage for an aligner, on which an object to be exposed is placed to be aligned and exposed.
2. Related Art
Printed circuit boards become thin as electric equipments become smaller and thinner. For example, a flexible circuit board has been developed and is becoming a common device since it is flexible and plastic to conform to the figure of casing of the electric equipments. These thin type of printed circuit boards have typically about 50 xcexcm thickness or less to about 25 xcexcm.
These printed circuit boards are produced by photolithographic method, where aligners that is similar to the one used in semiconductor integrated circuits producing are utilized for exposing circuit patters on the boards. It is needed in using the aligners to hold the printed circuit boards on an exposing stage. Typically the stage has hole to vacuum the board laid thereon and to hold it.
However the boards have been thinned as described above, there is a problem that the thin boards tend to be bent at the portion that touches the vacuum hole on the stage. Such bending of boards causes between a photo-mask and the board the gap that leads to many exposing troubles and to wrong resolution. The object of the invention is to resolve such problems.
The present invention is characterized by comprising a plurality of holes for absorbing the board having an aperture on the board stage and the suction means connected to the holes for absorbing the board, wherein said plurality of holes have such size that does not make the board bend, which causes exposing troubles when absorbing the board.
According to the inventor""s studies, the diameter of the suction holes must be less than 0.4 mm in order to prevent such bend that causes exposing troubles for the board of 50 xcexcm thickness that is average at thin type printed circuit boards. Such small holes can be produced easily and at low cost by photolithographic method.
When making small holes by photolithographic method, it is preferred to make holes on a metal plate and use it as a suction plate.
The metal suction plate on which the small holes are made is preferably supported by a supporting body having a suction space connected to the holes.
The suction space may be opened on the one face of the supporting body and the suction plate may be set on the face by gluing or the like.
The aperture of the suction space must be substantially small in order not to make on the metal plate such bending that causes exposing troubles when absorbing. However since the suction metal plate can be thicker than the printed circuit boards, for example it may be about 1 mm thickness, it is easy to form the aperture of the suction space at such size not to bend the suction plate.
Said supporting body may be provided with an air passage connected to the suction space and to the means for absorbing the board. The diameter of the air passage is preferably smaller than the suction space to keep the strength of the supporting body.